Toward Reservoir-on-a-Chip: Fabricating Reservoir Micromodels by in Situ Growing Calcium Carbonate Nanocrystals in Microfluidic Channels.

We introduce a novel and simple method to fabricate calcium carbonate (CaCO3) micromodels by in situ growing a thin layer of CaCO3 nanocrystals with a thickness of 1-2 μm in microfluidic channels. This approach enables us to fabricate synthetic CaCO3 reservoir micromodels having surfaces fully covered with calcite, while the dimensions and geometries of the micromodels are controllable on the basis of the original microfluidic channels. We have tuned the wettability of the CaCO3-coated microchannels at simulated oil reservoir conditions without introducing any chemical additives to the system; thus the resulting oil-wet surface makes the micromodel more faithfully resemble a natural carbonate reservoir rock. With the advantage of its excellent optical transparency, the micromodel allows us to directly visualize the complex multiphase flows and geochemical fluid-calcite interactions by spectroscopic and microscopic imaging techniques. The CaCO3-coated microfluidic channels provide new capabilities as a micromodel system to mimic real carbonate reservoir properties, which would allow us to perform a water-oil displacement experiment in small-volume samples for the rapid screening of candidate fluids for enhanced oil recovery (EOR). The immiscible fluid displacement process within carbonate micromodels has been demonstrated showing the water-oil-carbonate interactions at pore-scale in real time by fluorescence microscopic imaging.